London native David Jude Law slowly came up through the acting ranks like so many of his contemporaries: a stint at the National Youth Music Theatre, some work in British TV soaps, then lots of time on the stage. Things changed in the mid-90s when he scored a Tony nomination on Broadway for Indiscretions. Soon after, he had a solid costarring role in his first film Gattaca. Law considers landing his a part in The Talented Mr. Ripley to be his big break, or as he puts it, the turning point. Hes since gone on to play an automaton in A.I. Artificial Intelligence, a hideously scarred lout in Road to Perdition, a cad in Alfie, a different kind of cad in Sleuth, the great Dr. Watson in Sherlock Holmes and its sequel, and a cuckolded husband in Anna Karenina. In the new thriller Side Effects, he plays a workaholic psychiatrist whose newest patient (Rooney Mara) proves to be his toughest case. Law, 40, has already finished filming Dom Hemingway, is midway through The Grand Budapest Hotel, and will star in Henry V on the London stage this fall. He recently spoke about himself and his profession in Los Angeles.

What were your initial thoughts about how to play Dr. Banks in Side Effects?

I wanted to make it very clear that this guy was good at what he did, and was aware of the sense of boundaries, of when and how a situation may arise for a psychiatrist and where it will impact his or her private life. But were also telling a story. So as an actor, at some point you have to work out where the drama is best played out. As the story dictates, his life starts to implodes, so it was important to me to have a sense of him kind of crumbling. At the same time there was a beautiful subtlety to the story, where youre not sure whether hes got the upper hand or whether theres a time where you think hes going mad.

Did playing the part make you feel any differently about psychiatrists?

A lot of the discussion around this film is about the abuse of medicine or perhaps relying on medicine for all the wrong reasons. Of course medicine is used for a lot of good reasons, too. I kind of left this job feeling very respectful of psychiatry as a profession.

Is there a story behind the name Jude?

Im not really sure, but I believe it came from at least two sources: the book Jude the Obscure and the [Beatles] song.

Did you go to a lot of movies as a kid?

My father would take me to see The Wild Geese, Rocky, things like that. My mum would take me to see Ladri di biciclette and Padre Padrone.They introduced me to two very different styles of cinema, and I love both.

How did it feel to turn 40?

It was a liberating opportunity to cut off the shackles. When youre in your 20s, youre kind of built up to be the new it boy or the girl in the street and all that. In your 30s youre knocked down and knocked into shape. Forty to 50 to 60 I think are exciting decades. The parts are often more meaty. The concentration is often more on your acting than who you are and what you represent. I think thats a really exciting future, and thats all Ive ever really been interested in. So 40 is certainly a marker that I feel is talking me in the right direction.

Side Effects opens on Feb. 8.

Ed Symkus covers movies for GateHouse Media.